1. Field of the Invention
The present invention relates to a mobile body recognizing apparatus and a motor vehicle monitoring apparatus for detecting, with an image sensor such as an imaging device or the like mounted on a motor vehicle such as an automobile, information of another motor vehicle that approaches the motor vehicle from behind or laterally, as brightness information, calculating motion of the other approaching motor vehicle based on the detected information, and issuing a warning to the driver of the motor vehicle if the other approaching motor vehicle is predicted to pose a danger.
2. Description of the Related Art
The rapid advances in car electronics in recent years have created various computer-controlled technologies for assisting in safe driving of motor vehicles such as automobiles. The developed computer-controlled safety schemes include a system wherein road signs, nearby objects, and other motor vehicles are imaged by a CCD sensor, and the image signal from the CCD sensor is processed to recognize motion of those other motor vehicles.
It is assumed, for example, that a motor vehicle is approached by another motor vehicle from behind the motor vehicle, the driver of which tends to overlook objects behind the motor vehicle. If the driver makes a left or right turn or changes lanes without paying much attention to the other approaching motor vehicle, then the approaching motor vehicle has to be braked in order to avoid an imminent danger and hence is prevented from running smoothly. It is highly useful and advantageous from the standpoint of smooth traffic control to equip a motor vehicle with a function to be able to recognize another approaching motor vehicle.
Such a technology for recognizing motion of a mobile body is expected to be developed for use with various mobile bodies in general, including airplanes and ships as well as automobiles. The technology itself constitutes an important technical field that is believed to find a wide variety of applications in the future.
One conventional process of detecting the existence of a motor vehicle that is approaching another motor vehicle from behind and enabling the driver of the latter motor vehicle to recognize the detected approaching motor vehicle is disclosed in Japanese laid-open patent publication No. 7-50769, for example.
According to the disclosed process, an imaging device such as a video camera, a CCD (Charge-Coupled Device) camera, or the like mounted on a rear portion of a motor vehicle captures rear and side scenery image information, and a processor determines the level of a danger created by an approaching motor vehicle which attempts to pass the motor vehicle or is running in an adjacent lane, based on the captured image information, and issues a warning to the driver of the motor vehicle. Specifically, the processor detects, as an optical flow vector, motion of a point on an object in the images of two chronologically successive frames among a series of rear and side scenery images captured by the imaging device, and determines the level of a danger from the magnitude and direction of the optical flow vector.
In the above process, a window is established in radial directions from an FOE (Focus of Expansion) in a previous image, and moved in the same directions in a subsequent image. The centers of preset positions in the previous and subsequent images in the window are interconnected by an arrow, which is defined as an optical flow vector for a point in question. The speed and direction of a following motor vehicle in the images are determined from the magnitude and direction of the optical flow vector.
According to the above process of detecting a motor vehicle, it is necessary to recognize an image through image processing from image information obtained by an imaging device for thereby identifying a motor vehicle that follows a motor vehicle carrying the imaging device, and then to calculate an optical flow of the following motor vehicle in the image information of two chronologically successive frames.
Generally, identifying a certain motor vehicle, e.g., a following motor vehicle, from image information obtained by an imaging device requires a high image processing capability, and a processor for carrying out such image processing needs to be able to process a large amount of image information in a short period of time. Particularly, a high-speed processor capable of instantaneously processing a large amount of data needs to be installed on an automobile to perform a function to recognize, in advance, the existence of another automobile approaching from behind in an attempt to pass the automobile and then give a suitable warning to the driver of the automobile. Image processing software that is run by the above high-speed processor is required to have a highly sophisticated image processing algorithm, with the result that the high-speed processor is necessarily highly expensive to manufacture.
Even if the information obtained to recognize a following approaching motor vehicle is held to a minimum required amount in order to eliminate the above drawbacks, the processor needs to be able to detect the following approaching motor vehicle with good accuracy.
It is therefore an object of the present invention to provide a mobile body recognizing apparatus which is capable of reliably recognizing a mobile body such as a motor vehicle, for example.
Another object of the present invention is to provide a mobile body recognizing apparatus which is capable of holding information obtained from a mobile body to a minimum required amount and determining the status of the mobile body by effectively using the minimum required amount of information.
Still another object of the present invention is to provide a motor vehicle monitoring apparatus which is capable of holding information obtained from another motor vehicle that is approaching a motor vehicle to a minimum required amount and highly accurately determining the status of the other motor vehicle by effectively using the minimum required amount of information.